Many of these countries with single resources have to have some serious stockpiles of those resources. Since you won't let us produce more resources, why not let us loot them? In countries that have more than one supply of a given resource we could get a percentage of the stockpile according to how many supply sources they have. This would be more realistic to me than having all existing stocks of resources vanish when we take over another country.
I'm sure it would also alleviate some of the current pressure for higher resource production.
I'm sure it would also alleviate some of the current pressure for higher resource production.